Hydropneumatic automatic pilot



B .G. cARLsoN HYDROPNEUMATIG AUTOMAT I C P I LOT omginal Filedv June 19, 193e 2 Sheets-Sheet l INVENTOR Y BeYri G. Carl 07d MMM d@ H15 ATTORNEY Dea, 13, 193s. A B. G. CARLSQN 2,139,878

BHDROPNEUMATIC AUTOMATIC' PILOT originan Filed June A19, 19:56 2 sheets-sheet 2 E l BPH n l N "HHH" |NVENTOR "5 HIS ATTORNEYy Patented' Dee. 13,1938

UNITED STATES PATENT OFFICE 2,139,878 HYDRDPNEUMATIC AUTOMATIC'PILOT Bert- G'. Carlson, Freeport, N. Y., assignorto Sperryv Gyroscope Company, Inc., Brooklyn,

N. Y., a corporationlof NewYork Application June 19, 1936, Serial No. 86,036

Renewed February 18, 1938 21 Claims.

p This invention relates, generally, to hydropneumatic automatic pilots such as disclosed in my prior Patent #1,992,970, joint with E. A. Sperry and M. F. Bates, and tthev invention has reference, more particularly, to improvements therein involving a novel hydraulic` follow-up and level flight control means.

In the disclosure of the above patent and in similar devices heretofore used, mechanical follow-up connections such as links or cables ex-v tend from the hydraulic servomotors or from the control surfaces-to the controlling gyroscopes or other control unit or position maintainingfmeans, that are generally located on the pilots dash. It is desirable, in order to reduce the length of control surface operating cables to a minimum, to place the servomotors as nearsthe control surfaces actuated thereby astpossible. Hence, the mechanical followup connections are generallysomewhat lengthy and therefore not only complicate the system but may become deranged in use.-

'Ihev principal` object of the present invention is to provide a novel hydraulic follow-up for automatic pilots, which follow-up is so constructed and arranged as to adapt the same to be located at theA master hydraulic valve adjacent the controlling 'gyroscope, thereby -eliminating long lengths of mechanical follow-up connections and simplifying the automatic pilot apparatus, While enhancing the reliability of the system in use.

Another objectof the present invention liesin the provision of a novel hydraulicl follow-up of the above character, wherein movement or pressure of the operating fluid discharged from the servomotoi` during the operation` of a control surface is employed 'for operating the hydraulic follow-up means.

lStill another object of the present invention is to `provide means cooperable with said hydraulic follow-up for maintaining the aircraft at approximately any desired ying level regardless of changes in the position of the center of gravity of the craft due, for example, t movement of passengers, and regardless of changes in weight of the craft due, for example, to the consumption Of fuel. I I

Other objects and advantagesl will'become apparent from the specification, taken in connection with the accompanying drawings wherein one embodiment of the invention is illustrated.

In the drawings, Fig. 1 is a schematic view, largely in section,

. 'illustrating the4 improvements" 'of this invention.l

Fig. 2 is a detail View, largely in section, of the structure of Fig. 1. p I

Fig. 3 is a view in front elevation, with parts broken away, of the gyro vertical or artificial horizon unit shown in Fig. 2.

1 Similar characters of reference are used in the above views to indicate corresponding parts. Referring now to the said drawings, the reference numeral I designates the gyro vertical or articial horizon unit of the automatic pilot, although this invention is equally'applicable to the directional gyro unit, or any other position, attitude or direction maintaining device, the latter being omitted for the sake of simplicity. The unit I comprises an air spun gyro (not shown) mounted for spinning on a vertical axis within rotor bearing casing 2, Which in turn is pivoted on horizontal trunnions 3 in gimbal ring 4. -Rng 4, in turn, is mounted for oscillation on horizontal pivots 5in the main frame 6. In order to take olf controls from both axes, there is shown a circular bail or loop 'I pivoted on trunnions 8l in main frame 6, said trunnions being preferably normally in line with the trunnions 3l Loop 'I has a rolling contact with a roller 9 at the bottom of the gyroscope, which is guided between U-shaped sides of the loop. The loop 1,

therefore, partakes of the oscillation of the gyroscope `about minor axis 3, 3, but not of its oscillation about its major axis' 5, 5.

Loop or bail 'I has secured to one end thereof a semi-circular shutter I0 provided with horizontal knife edges II which normally bisect horizontal `apertures I1 in casing I8 surrounding a flexible diaphragm I9, which air iioWs through. pipes 20 and 26 tothe ports,|2 and I2', respectively.

Similarly, there is provided asemicircularl shutter I9' secured toA the'gimbal 4, cooperating with similar, air ports I4 and I4'4 provided in a common. frame memberv I5 pivoted on thev main frame 6 for controlling the ailerons of the` craft.'

Ports I4 and I4 are similarly supplied with air' 'from pipes connected to the casing of a second diaphragm (not shown) similar to diaphragm I9.

The structure so far described is similar to that disclosed 1nA the aforesaid Patent #1,992,970, and' hence requiresv no further description.

The exible diaphragm I9 is connected to the balanced piston 22 movable within thebore 35 of a master hydraulic valve 2| located adjacent the gyro unit Valve 2| is adapted to control the supply of pressure operating fluid through pipes 24 and 24 to servo motor 23, having an operating piston 21 connected through cables 28 and 28' for operating the elevator or elevators 25. Preferably, `the servomotor 23 is located as near the control surface or elevator 25 as possible to reduce the length of transmission cables 28 and 28', or equivalent means, to a minimum, the

only connection between the remote servo motor.

23 and the valve 2| being pipes 24 and 24', the elevator hydraulic follow-up connection being removed from the servomotor 23 and elevator 25 and being associated with the master control valve 2|. Valve 2| is adapted to receive pressure fluid, such as oil,from suitable pump means 28 through pipe 29, the return of pressure fluid to pump 28 from valve 2| being through pipe 38 or pipes 3| and 38.

Valve 2| is shown diagrammatically in Fig. 1 and more invdetail in Fig. 2, the parts being correspondingly numbered. The slide rod or piston valve proper 22 is shown as having a central collar or piston normally overlying intake port l29' from pipe 28 leading to the pump, spaced collars 14 and 14 normally covering ports 33 and 33' leading to the hydraulic follow-up cylinder 32, and end collars 88 and 88. In addition to the ports mentionedabove, bore is provided with ports 8| and 8|' normally between collars 13, 14 and 13, 14', respectively, and connected with pipes 24 andV 2 4 leading to servo cylinder 23. A second pair of ports 82 and 82 between co1- lars 14-80 and 14'-80' are both connected to the return pipe 38, ports 82 and 82' being cross connected through dotted passage 83. An outer drain port 84 may also be provided to drain back the oil that leaks past the collars into return pipe 3|, said port being connected to the outer end of -rod 22 through an aperture 85 through the rod. A needle valve 85 is shown in one of pipes 24, 24' to regulate the rate of oil ow to the servo cylinder.

The hydraulic follow-up comprises a cylinder 32 preferably mounted directly upon the master hydraulic vnive 2| and having. its end portions connectedlthrough passages 33 and 33 to the bore 35 of valve 2|. A follow-up piston 36 is movabiewanin the bore 4| of cynnder az and has a piston rod 38 extending outwardly of cylinder 32 for connection to the shaft 39 of a worm 4l within gyro unit I. Centering springs 42, contained within bore 4| and engaging follow-up piston 38, tend to retain this piston in centered position within cylinder 32, Awhile centering springs 43 within the valve 2| serve to center the balanced piston valve 22. y

Y A by-pass passage 44 is provided around follow-up piston 38, which passage is restricted by a suitable valve such as the valve 45, shown as a needle valve in Fig. 1 and as a plug valve in Fig. 2, the plug or needle valve having a small opening 48 for by-paing or bleeding pressure uid at the desired rate. Obviously, the valve may be left closed, if desired. Bore 4| of the hydraulic follow-up cylinder.` has the same uid capacity as the servo motor cylinder 23 and, as will further appear, working fluid discharged from cylinder 23 flows into bore 4I for actuating the follow-up piston 38 and,'but for the small leak through by-pass valve 45, i. e. if the by-pass valve is closed, the piston 38 would' have a movement equal or proportional to that of theservo motor piston 21.

Worm 48 meshes with a gear segment 48 that is xed upon frame member I3. Worm 48 has a longitudinal bore for slidably receiving a shaft 48 that is splined to worm 40 as by slot and pin means 48. A spring pressed clutch disc 58 is splined on shaft 48 and is urged by spring 5| into engagement with a gear 52 carried by a hub 53 journaled in the forward wall 54 of gyro unit I. A knob 55 positioned in front of wall 54 has a stem 58 journaled in hub 53, which stem carries a cross-pin 51 adapted to engage a conforming recess in the end of shaft 48 when the knob 55 is pushed rearwardly, thereby coupling knob 55 and stem 58 to shaft 48. In pushing knob 55 rearwardly, the cross-pin 51 also ,engages clutch disc 58 to disengage this clutch disc from gear 52.

Gear 52 meshes with a gear 58 journaled on a iixed support 59. A Bourdon tube '88 has one end fixed to gear 58 and its other end fixed -to support 59, and is connected by ,a pipe`8| to a diaphragm casing 82 containing a flexible diaphragm exposed to the atmosphere, vwhereby gear 58 is caused to turn in response to changes in atmospheric pressure due to changes in altitude of the aircraft. If desired, the pipe 8| could be connected to the intake manifold of the aircraft engine, wherein the air pressure is also variable in response to ascent or descentof the craft.

A turnable indicator cylinder 63 is located behind a window 84 provided in the front wall 54 and has its hub 81 connected by a flexible connector or tape 85 to the hub of a gear 68, meshing with worm 48. Connector 85 has one end fixed to the hub of gear86 and extends down and around the hub 81 -of cylinder 83 and has its other end attachedto a spring 88 that is anchored and serves to tension connector 85. fThe surface of cylinder 83 is marked with vangle indications 69 for indicating the fore and aft tilt of the aircraft with respect to the horizontal.

Although the master control valve 2|, servo motor 23 and hydraulic follow-up have been described in connection with the control of the elevator 25, it will be understood that similar equipment is provided for the ailerons and rudder of the aircraft. Thus, the air pick-Gif, including ports vI4 and i4 of frame member I5, is connected by pipes 10 to a flexible diaphragm casing '(not shown) having a diaphragm connected to a master control valve for controlling the supply of pressure operating fluid to the aileron servo motor. Likewise a similar control ls taken off the directional gyro for controlling the crafts rudder. It may be noted also that While followback piston 38 directly controls the pick-off valveports Ill-I2 at the gyroscope, themovement vof said piston secondarily restores the relay valve, since restoration of the controller equalizes the air pressure in'chamber I1, permitting centralizing' springs 43 to restore the relay.

In use, although thel automatic pilot maybe used in an airplane as the sole control means, it would ordinarily be employed as an adjunct to the usual manual controls, in which case the aviator may instantly take over the lcontrols from Fig. 1). artificial horizon and directional gyroscope in the lusual manner.y To cutin the automatic controls,

the craft is brought onto an even keel on a set course and the air and oil pumps I8 and 28 The aviator may then steer from the started working. the knob 55 having been prevl- 7|,

ously adjusted, if necessary, so that scale 69 indicates zero inclination. The corresponding scale 69' of the aileron control associated with control knob 55' (see Fig. 3) should also be brought to zero before cutting in the automatic control and with the horizon bar showing zero transverse inclination. Likewise the corresponding scale of the directional gyro (not shown) should be brought to zero.

With the automatic control working, longitudinal and lateral stabilizing of the airplane will be maintained through the ports I2, I2'l and It, I4', respectively, on the gyro vertical I, While the set course will be maintained through the functioning of the corresponding air ports on the directional gyro. Thus, assume, for example, that the airplane starts to ascend for any reason due, for instance, to movement kof passengers within the plane cabin or to the shifting of the center of gravity of the plane due to fuel consumption. In such case, since the frame member I3, carrying ports I2 and I2', turns yclockwise with the craft while the shutter knife edges I I controlled by the'gyro vertical remain horizontal, the port I2 is uncovered and port I2 is covered by shutter It, resulting in the cutting o of the suction on pipe 20 so that diaphragm I9 is deflected toward the right, as shown in Fig. 1. Movement of diaphragm I9 causes piston valve 22 to move from its central position shown in Fig. 2, in which position supply pipe 29 is blocked by valve portion I3 while passages 33 and 33 -are blocked by valve portions 'Idand Ill', toward the right into the position shown in Fig. .1. In this latter position of the valve, pressure fluid from pump 28 flows through pipe 29, into valve borev wardly and causing downward turning of elevator 25 from its horizontal position to correctl through. pipe at' so that fluid from this pipe passes into valve bore 35 and thence through passage 33 into the cylinder 32, causing the hydraulic follow-up piston 35 to move toward the left from its centered position, thereby moving piston rod 3B and hence worm it toward 4the left so that gear segment 65 and ports I2 and I2' are turned counter-clockwise due to the combined movement of worm i0 and that of the craft under the action of control surface 25. 'I'his movement of ports I2 and I2 results in the covering of port I2 and the uncovering of port I2 so that diaphragm I9 is moved toward the left, causing master control valve piston 22 to move toward the left, effecting the'elevation of elevator 25 so that, as the craft again assumes an even keel, the elevator 25 will again be substantially though not quite horizontal, the action of by-pass valve 45, when used serving to cause elevator 25 to return to a position slightly depressed froml the horizontal, thereby providing a permanent correction for the tendency of the craft to climb.

'Ihis action of the follow-up by-pass will be evident when it is noted that as the elevator 25 was being depressed by upward movement of piston 21, the movementof follow-up piston 36 was not quite equal or proportional to that of piston 2l due to the slight leakage of fluid through bypass 44 around piston 36 so that the ports I2 and I2 were not turned back as much as they would otherwise have been, so that after correction, the piston 21 is left slightly above central position in cylinder 23 with the elevator 25 slightly de` pressed while the ports I2 and I2 are horizontal.

If, in spite of this permanent elevator correction, the craft should still tend to ascend, the automatic operation of the elevator will be repeated, correcting for the ascent and leaving the elevator- 25 depressed somewhat more than it was4 after the initial correction. In this way, after one or more operations of the servo motor 23, the craft is held on an even keel without repeated and subsequent operations of the servo motor, which intermittent operations would otherwise be n cessary if the by-pass M were not present. In lie manner, the system automatically corrects for any tendency of the craft to descend without repeated operations of the control surface serv'o motor. I f

When it is desired to make the craft climb or descend, it is merely necessary to press the knob 55 in slightly, thereby releasing clutch disc 50 while coupling stem 55 to shaft @8,v and then turn the knob and hence shaft ad in the proper direction to Aeect the desiredv maneuver. As shaft t8 is turned, the worm I0 turns gear segment i6 to move ports I2 and I2' and hence eect operation of the elevator. By turning knob 55', a similar control Lof-the'ailerons'is obtained and by turning the corresponding knob on the directional gyro, the course of the craft may' be changed as desired. A

Since gear 55 is cconnected through worm il@ to gear segment ti, gear @e turns in response to the .turning of ports I2 and-I2', and hence the reading of the angle indicator 69 on cylinder 53 with respect to mark I2 gives the inclination of the fore and aft axis of the craft rwith respect to the horizontal, while the reading of indicator te with respect to mark I2 gives the transverse inclination of the craft with respect lto the horizontal, and the corresponding indicator of the directional gyro gives the deviation of the craft from its course.-

The Bourdon tube 6U also acts to aid in maintaining the craft at any desiredaltitude' during night. Thus, should the craft start to ascend due,

for example, to the consumption of fuel, the reduction in atmospheric pressure resulting from' As many changes could be made in the above y construction and many .apparently Widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and movements of the control surface.

2. In automatic pilot for aircraft, the combination with a position maintaining means, of differential air flow means actuated by relative turning of the cra-ft and means, a hydraulic servomotor system having a servomotor for operating a control surface, a pneumatically operated hyhydraulic valve operated from the differential air pressure created by said means for controlling said servomotor, and a hydraulic follow-up from said valve to said means, whereby mechanical lfollow-back from said surface to said means is eliminated.

. 4. In an automatic pilot for aircraft, the combination with a control unit, a differential air ilow means actuated by relative turning of the craftand unit, a hydraulic servomotor for turning a control surface, a pneumatically operated hydraulic valve operated from the differential air pressure created by said means for controlling the supplyof pressure operatingfiuid to saidservomotor, and a hydraulic follow-up positioned adjacent said unit and supplied with operating fluid exhausted from said servomotor for acting upon said means in accordance with movements of the control surface.

' 5.* In an automatic pilot for aircraft, the combination with a position maintaining means, a differential air flow means actuated by relative turning of the craft and means, a hydraulic servomotor for turning a control surface, a pneumatically' operated hydraulic valve operated from theI differential air pressure created by said means forl controlling the supply of pressure operating fluid to said servomotor, a hydraulic follow-up positioned adjacent said means and supplied with `'operating fluid exhausted from said servomotor for acting upon said means in accordance with movements of the control surface, and means for by-passing a portion of theoperatlng fluid exhausted from said servomotor, whereby the control surface i's caused to assume a new position of reference.

6. In anautomatic pilot for aircraft, a stabilizing gyroscope, hydraulically operated means controlled from said gyroscope for controlling the ailerons and elevators, hydraulic follow-up means located adjacent said gyroscope and respectively controlled from said respective means, and bank and pitch indicators at said gyroscope connected to said respective follow-up means to be operated in accordance with movements of said ailerons and elevators.

7. In a control system for aircraft, a hydraulic pressure source, servo means connected with said source for actuating a control surface, air flow means, means pneumatically connected 'to said.

air flow means and responsive to pressure changes, a control valve actuatedV by said last named means for controlling the supply of pressure uid from said source to vsaidservo means,

analtitude control unit for differentially effecting pressure changes in said control valve actuating means,- and follow-back means to saidunit operated ,from said valve.

8. In an automatic control system for aircraft, the combination with a gyroscope, of means for automatically controlling a control surface therefrom comprising a hydraulic pressure source, means for actuating said surface connected with said source, a valve for controlling thev connection between saidsource and said surface actuating means, air circulating means, a differential air Ipressure diaphragm for controlling said valve,

means having differential air flow ports connected with said diaphragm and s'aid circulating means and movable with the -aircraft relative to said gyroscope, whereby differential pressure changes are effected on the two sides of said diaphragm, and follow-back means from said valve to said 'port means.

having differential air flow ports connected withv said diaphragm and said flow means and movable with the aircraft relative to said gyroscope, whereby differential pressure changes are effected on the two sides of said diaphragm, and followback means'from said valve to said port means,

said follow-back means comprising a hydraulic cylinder connected to said valve, and a piston movable Within said cylinder and connected to said port means.

10. In an automatic control system for aircraft, the combination with a gyroscope, of means for automatically controlling a control surface therefrom comprising a hydraulic pressure source, means for actuating said surface connected with said source, a valve for controlling the connection between said source and said surface actuating means, air :dow means, a differentialair pressure diaphragm for controlling said valve, means having differential air flow ports connected with'said diaphragm and said flow means and movable with .the aircraft relative to said gyroscope, whereby differential pressure changes are effected on the two sides of' said diaphragm, and follow-baci:`

means from said valve to said port means, said follow-back means comprising a hydraulic cylinder connected to said valve, and a piston movable within said cylinder and connected to said port means, the connection between said piston and said port means including differential means to provide for simultaneous independent operation of said port means.

bination with a gyroscope, a controller actuated by relative turning of the craftand gyroscope, a

hydraulic servo motorfor turning a control sur- 11. In an automatic pilot for aircraft, the combination with a gyroscope, a controller actuated by relative pitching of the craft and gyroscope, a iiuid servomotor for turning a control surface, a fiuid relay valve operated from said controller for controlling said 4servomotory-a fluid follow-up from said valve to said controller, said fluid follow-up having a restricted by-pass, and means responsivev to altitude variations arranged for connection to aisasvs v I said controller for maintaining the aircraft at a desired altitude.

13. In an automaticl pilot for aircraft, the combination with a direction maintaining means such as a gyroscope, a controller thereat rendered operative upon relative turning of the craft and said means for turning the rudder, a relay device directly operated by said controller and positioned adjacent the same, a, rudder operating servomotor operated by said device and adapted to be located adjacent the rudder and remote from said controller, and a followup means at said device constructed and arranged to move proportionally to said servomotor for imparting a follow-up movement to said controller without a mechanical connection to said servo motor or rudder.

14. A follow-up means for automatic pilots as claimed in claim 13, wherein the servomotor and relay'comprise a. hydraulic piston and slide valve respectively,.and said follow-up means comprises a second hydraulic piston adjacent said slide valve and located in series with said valve and said drst named piston. y 15. In an automatic pilot for aircraft, the combination with an attitude control unit such. as a gyroscope, a controller` actuated by relative turning of the craft and unit, a source of hydraulic pressure, a hydraulic piston and cylinder for turning a control surface, a valve operated from said controller'for controlling the uid ilow to and from said source and said piston, and a -hydraulic follow-up piston and cylinder adjacent said controller in series with said first named cylinder, its control valve and said source, whereby a follow-back connection from. the control surface to said controller is provided through the hydraulic systemv and `withoutmechanical follow-back connection. A

416. In an automatic pilot for aircraft, the combination with an attitude control unit such as a gyroscope, a controller actuated by relative turn-- ing of the craft and unit, means governed by said controller for causing duid dow in a closed system, said system including a pair of spaced servo Acylinders connected in series in said duid system, and a control surface, one of said cylinders being j adjacent said surface and operating the same, and said other cylinder being adjacent said unit andA operating f as a follow back connectie! thereto. f

17. In an automatic pilot for craft, direction maintaining means, a fluid pressure relay actuated Aby said means, .a duid pressure servomoto: controlled by said relay, and means associate: with said relay subject to the duid pressure il said servomotor. for restoring said relay to neutral position.

18. In an automatic pilot for aircraft. thi combination with an attitude ntrol unit sucl as a gyroscope, a controller actuated by relativi turning of the craft and unit, a relay controlle from said controller for causing duid flow` in I closed system, said system including a pair o: spaced servo cylinders connected in series in sak duid system, and a control surface, one of sai: cylinders being adjacent said surface and open ating the same, and said other cylinder being ai said relay and operating to restore the same tu neutral position. t

19.- In an automatic 'pilot for craft, directie: maintaining means, a duid pressure relay actuated by said means, a duid pressure servomotox controlled .by said relay. means responsive t1 duid pressure acting on the servomotor for re storing said relay, and means-forbiasing sais restoring ymeans toward its neutral position.

20. In an automatic pilot for craft, directie! maintaining means, `a duid pressure relay actuated by said means, a duid pressure servomotoi controlled by said relay, means lresponsive t1 v duid pressure acting on the servomotor for re storing said relay, means for biasing saidrestorI ing means toward its. neutral position, and n bleeder for slowly diminishing the eifective dull pressure acting on said restoring means.

tively to said chamber.

BERT G. GARIBQN. 

